RDMA/mlx5: Store ndescs instead of the translation table size

RDMA/mlx5: Store ndescs instead of the translation table size

Currently, ent->xlt stores the translation table size. This data should
not be stored in the cache entry but be written directly to the mailbox.
Store ndescs instead, and deduce the translation table size from it
according to the access mode.

Link: https://lore.kernel.org/r/e9dbfaa1f279793a6bd28ee5a31cb4f0f0d70f05.1644947594.git.leonro@nvidia.com
Signed-off-by: Aharon Landau <aharonl@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>